Note: Descriptions are shown in the official language in which they were submitted.
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2156644
METHOD AND APPARATUS FOR CONTINUOUS GALVANIC OR CHEMICAL
APPLICATION OF METALLIC LAYERS ON A BODY
The invention is. directed to a galvanic process for
galvanic or chemical treatment, in particular for the
continuous application of metallic layers on a body, and to a
device for implementing the process.
It is known in theory that the deposition rate in
electrolytic transfer of material increases in proportion to
increasing current densities. In practice, however, a
diffusion layer form~~ at the cathode as current densities
increase, since the transfer of matter between the anode and
cathode is slower than the deposition rate of the ions in the
immediate vicinity of. the cathode. Thus the greater the
selected current den:~ity applied, the greater the diffusion
layer around the cathode and the slower and less complete the
deposition rate of the ions on the cathode. Beyond a
determined reaction :peed, the delivery of metal ions at the
phase limit between t:he material transfer region and charge
passage region can no longer compensate for the consumption at
the cathode. Therefore the current density/deposition rate
curve exhibits an asymptotic limiting value which occurs, as
mentioned above, due to the electrically insulating diffusion
layer resulting from insufficient supply of matter.
Electrolyte movement can provide a solution. As experiments
have shown, the thickness of the diffusion layer decreases as
the intensity of ele~~trolyte movement increases. On the other
hand, metallic deposits became rough and powdery when the
selected current densities approach the theoretically possible
limiting current densities. Therefore, in order to obtain
satisfactory coating qualities, it is necessary to select
current densities which lie far below the possible limiting
current density and which, as a rule, amount to roughly only
one third of the limiting current density.
In zinc deposition especially, an increased current
density leads to unusable zinc deposits at the body which is
2156644
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to be coated owing to the present diffusion layer and the
resulting poor transfer of matter. If a zinc anode is used in
addition to the zinc ions in the electrolyte so as to maintain
constant the percentage of metal ions for the duration of the
galvanizing process, passivity effects occur at the zinc
anode, since the anodic current density increases at the anode
due to the dissolution process at the anode.
Arranging metal anodes on both sides of the cathode also
does not lead to an ~~_mprovement because this produces
eccentric deposits.
DE 34 39 750 A1 (published April 30, 1986} discloses a
process in which the electrolyte solution is moved in the
direction opposite to the movement direction of the body to be
coated in order to increase the deposition rate of coating
materials to be applied by electrodeposition. The sum
velocity resulting air the surface of the body to be coated
from the two different speeds lies in the range of turbulent
flow.
Although the thickness of the diffusion layer is reduced
in this manner by a turbulent flow, the decomposition of the
diffusion layer is insufficient. This is demonstrated, for
instance, already by the fact that an upper limit of 80 to 90
A/dm2 for the current: density to be applied may not be exceeded
in this location. Therefore, there continues to be a
diffusion layer of 10 to 15 ~, at this location on the body to
be coated.
The object of the present invention is to provide a
solution to this problem by means of an improved galvanic
process and a device for carrying out the process which
enables the diffusion layer between the electrolyte and the
body to be coated to be dissolved virtually completely and to
shift the asymptotic limiting value of the deposition rate
curve upward in order to reduce the coating time substantially
and to improve the g.uality of the metal coating.
3S In accordance with one aspect of the present invention
there is provided a process for the continuous deposition of a
metal layer on a substrate, comprising the steps of (A}
CA 02156644 2001-07-06
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connecting the substrate to a current source such that the
substrate acts as a cathode; (B) passing the substrate
longitudinall:~ in the negative x-direction through an
electrolyte comprising ions of the metal to be deposited, the
electrolyte being contained in a hollow body, wherein the
hollow body is connected to the current source such that the
hollow body acts as an anode; (C) injecting the electrolyte
into the hollow body, wherein the electrolyte is injected so
as to form a =jet that is inclined at an angle to the xy-plane,
and the direct=ion of flow of the electrolyte is in the
positive x-direction, i.n such a way that turbulent flow occurs
at the surface of the substrate and a diffusion layer at the
surface of the substrate is substantially eliminated; and (D)
regulating the current source to produce a current density at
the surface oi. the substrate of from about 10 to about 400
A/dm2 .
In accordance with ;mother aspect of the present
invention there is provided a device for the continuous
deposition of a metal layer on the surface of a moving linear
substrate, the device comprising a current source; a hollow
body connected to the cu:=:rent source as anode, the hollow body
in use containing a flowing electrolyte comprising ions of the
metal to be deposited, thc~ hollow body being adapted so that
in use, the linear substrate, which acts as a cathode, can
pass in a first end and out a second end; nozzles directed to
the interior cf the hollow body, for injecting jets of the
electrolyte, the jets impinging on the substrate at an acute
angle to the surface of the substrate and at an angle to the
longitudinal axis of the substrate, such that in use, the
electrolyte flows in a direction that is opposite to the
direction of motion of the substrate'; whereby turbulent flow
is created at the surface of the substrate, thereby
substantially eliminating a diffusion layer at the surface of
the substrate, and allowing a current density of from 10 to
400 A/dm2 to bf~ attained, when the device is in use.
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As a result of the virtually complete dissolution of the
diffusion layer, the process according to the invention
enables an increase i.n the deposition rate while at the same
time improving the coating quality in the selected operating
range of the current density/deposition rate curve.
As a result of t:he inventive construction of the nozzle
body acting as insoluble anode and the swirl inclination of
the nozzles for the delivery of the electrolytes, the flow
strikes the treated body uniformly on all sides regardless of
its diameter or surface qualities. By partially modifying the
flow along the body in a stepwise manner, not only is a
pressure drop prevented in the injected electrolyte with
respect to the length of the body to which it is applied, but,
further, as regards t:he galvanizing process, a flow of
electrical current i:~ achieved which acts on the body in a
pulsatile manner. This is achieved in that the diaphragms act
as throttling locations at which the flow rate increases,
which results in increased flow with respect to the transfer
of matter. As a result of the directed flow against the body
which is effected on all sides at high velocity and also as a
result of the partial change in the flow rate, the diffusion
layer is destroyed v_Lrtually completely along the
aforementioned surface of the body so as to ensure a trouble-
free transfer of mati~er to the cathode.
Further, the body to be treated is automatically centered
in the nozzle body v:ia the flow effect of the diaphragms so as
to ensure a uniform geometrical distance of the body from the
inner wall of the no;azle body. Uniform layer thickness is
achieved and short circuits are prevented in this way.
Moreover, it is ensured that the metallic coating applied to
the body is not damaged mechanically.
Whereas the pro~~esses of the prior art for galvanization,
e.g., galvanic zinci,ng, have a maximum current density of 80
to 90 A/dm2 at the surface of a body to be coated, the process
according to the invention, e.g., in galvanic zincing, allows
a current density of 10 to 400 A/dmz. Thus the deposition rate
4a 215b~44
is roughly three to five times greater compared with the prior
art.
The diaphragms i.n the form of annular disks made of
nonmetallic, electrically nonconductive material such as
plastic or ceramic make it possible to optimize the pulse
width and pulse frequency of the flow of electric current
acting on the body to be galvanized by selecting the relative
distance between the diaphragms and selecting their inner
diameter while taking into account the diameters of the outlet
openings of the bore holes, and by selecting their quantity -
throughput of electrolytes - as well as. their thickness. When
electrically conductive material is used for the diaphragms,
other electrical fie7_ds occur in the electrolyte and
accordingly other types of coating are also formed.
Similarly, this is ti:ue also with an alternating arrangement
of diaphragm materials. Accordingly, as experiments have
shown, metal alloys and predetermined textural structures can
be electrodeposited, which was not possible previously.
Depending on the desired production time and quality of
the metallic layer o~_~ its thickness, it is possible to arrange
an optional number oi= devices according to the invention one
after the other in series .
DE 33 17 970 A1 (published November 15, 1984) describes a
process for local electroplating of a printed circuit board by
means of electrolyte: exiting from two oppositely located
nozzles (see page 7, lines 11 to 13, of reference). The
printed circuit board is moved past the nozzles in a manner
similar to flow soldering in order to achieve a sheet-like
coating, the electro:Lyte being fed to the nozzles from a tub
and applied via the nozzles for this purpose. Thus the
nozzles serve exclusively to achieve the desired partial
coating of the printed circuit boards and not to increase the
output velocity of t:he electrolyte. Therefore the problem of
dissolving a diffusion layer by means of a final velocity of
the electrolytes frovm the sum of the velocity vectors for the
purpose of generating a turbulent flow is not addressed and
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accordingly not indicated in this reference.
The invention is described in the following with
reference to an embodiment example shown in the drawings.
Fig.~l shows an arrangement for galvanization with a
device according to the invention;
Fig. 2 shows a longitudinal section through an embodiment
example of a device for carrying out the process according to
the invention with a r.~ozzle body having a central through-bore
hole and a plurality of nozzle bore holes in the region planes
orthogonal to the central bore hole, which nozzle body
encloses a body to be coated, and with a hollow body serving
for the feed of the electrolyte;
Fig. 3 shows a front view of the device according to
Figure 2;
Fig. 4 is an enlarged view of a detail from Figure 2.
Figure 1 shows a work vessel 12 which is located in a
process vat 10 and which receives devices 14, to be described
in the following, for galvanization or chemical treatment,
according to the embodiment example, for continuous
application of a metallic layer on a body 15 which is
continuously guided through the work vessel 12 and devices 14,
the body 15 being constructed in the shape of a rod in the
present case.
An electrolyte 1~, located in the process vat 10 is fed
via a pump 16 to the individual device 14 via a pump line 19
and a feed 20 in the form of pipe connections. The exiting
electrolyte flows back: into the process vat 10 in the
direction of arrow 17. The flow rate of the electrolyte can
be influenced by the ~>ump.
One of the devices 14 is shown in an enlarged view in
Figure 2. As will be seen from the drawing, the electrolyte
18 which is introduced via the feed 20 flows through the
device 14 and passes, via a hollow body 30, into a nozzle body
34 in a manner to be described in the following. As is
indicated by the individual arrows, the electrolyte flows from
the nozzle body 34 back into the work vessel 12 and then into
the process vat 10.
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As will be seen from Figures 2 and 3, the device,
designated in its entirety by 14, for continuous galvanizing
of wires, outer surfaces of pipes or the like bodies 15
comprises the hollow body 30 through which the electrolyte 18
flows, this hollow body 30 forming a pressure vessel and
having two end sides 31 and 32, and the nozzle body 34 which
is constructed as a hollow body and is arranged coaxially to
the hollow body 30. The nozzle body 34 and the hollow body 30
have a common central through-opening 35. The nozzle body 34
is coated on all side; by an insoluble metallic layer 38 of a
metal from the platinum group. This metallic layer 38 also
covers the end sides 31 and 32 and the inner surface area of
the hollow body 30 and has a thickness of 2 to 20 ~. For the
sake of clarity, Figure 2 shows only the through-bore hole 35
with the metallic layer 38. In this way, it is ensured that
the effective surface~~ of the nozzle body 34 will not impart
metal ions to the electrolyte 18.
The feed 20 is connected with the surface area of the
hollow body 30 and is constructed as a pipe connection 24
which opens out tangentially - see Figure 3 - and which is
connected with a flana~e 22 of the pump line 19 via a union nut
23. An O-ring seal 25~ is arranged between the flange 22 and
the pipe connection 24. Thus the pump line 19 is connected
with the pipe connection 24 so as to be detachable but also in
a sealing manner.
The nozzle body 34 has a plurality of bore holes 44
distributed uniformly along its entire circumference. These
bore holes 44 are arranged so as to be distributed at equal
distances with reference to cross-sectional regions 11
extending vertically t.o the longitudinal axis 16 and extend so
as to be inclined at identical angles a and at a swirl angle
- see Figures 3 and 4 - relative to the body 15 to be coated
and opposite to the throughput direction of this body 15 which
is guided centrally through the nozzle body 34. An
electrically nonconductive guide ring 26 is arranged at the
outlet side 25 of the nozzle body 34.
As is shown in Figure 3, the axis of symmetry 41 of the
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pipe connection 20 is offset parallel to and eccentrically at
a distance (a) relative to the transverse axis 40 of the
device 14. As a result, the electrolyte 18 which is pumped
into the hollow body 30 enters the hollow body 30 in such a
way that its flow behavior remains unperturbed as far as
possible and flows around the nozzle body 34. The inlet
openings of the bore holes 44 are situated on flanks 46 of the
outer surface area of the nozzle body 34 which form part of
constricted portions 47 which are situated uniformly one after
the other and are V-shaped in cross section. The pumped in
electrolyte 18 flows into these constricted portions 47 and
subsequently, without loss of pressure, into the bore holes 44
and, via the outlet openings 37 acting as laval nozzles, into
the space of the through-opening 35. Diaphragms 36, each of
which has a through-opening 37, are inserted into the through-
opening 35 of the nozzle body 34 so as to be offset in the
longitudinal direction relative to the cross-sectional regions
11 in planes A to E which intersect the longitudinal axis 16
at right angles.
One of the diaphragms 36 formed from electrically
nonconductive material. is shown in Figure 4. For certain
applications, these diaphragms 36 can also be formed from an
electrically conductive material or can be arranged
alternately as electrically conductive and electrically
nonconductive materials. The through-flow opening 37 of the
diaphragms 36 is enlarged in cross section in a stepwise
manner with reference to the through-flow direction of the
electrolyte which is directed opposite to the throughput
direction of the body 15 to be coated so as to prevent a
pressure drop in the nozzle body 34. Thus the smallest
through-flow opening 37 is located in plane E, while the
largest through-flow opening 37 is located in plane A. As is
shown in Figure 4, the: diaphragms 36 have a plurality of
swirl-producing notches 39 aligned tangentially to the
through-opening 37.
The described device operates in the following manners
The body 15 to be coated is connected to the negative pole of
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a current source, not shown, e.g., via current-carrying
contact rollers, while: the nozzle body 34 is connected via
current rails 13 with the positive pole of the current source,
not shown. The current density is regulated to 10 to 400
A/dm2, corresponding to the process to be carried out, via
circuit elements, known per se.
The inherent velocity impressed on the body 15 to be
coated acts in the throughput direction. The electrolyte 18
which is under pressure between the hollow body 30 and nozzle
body 34 passes through the bore holes 44 of the nozzle body
34.
The electrolyte 1.8 delivered via the pump 16 is
accelerated as it flours through the bore holes 44, since these
bore holes 44 act as Laval nozzles, and is injected so as to
be inclined at an angle a to - and opposite the throughput
direction of - the body 15 to be coated, as well as at a swirl
angle Vii. As a result of the uniform arrangement of the bore
holes 44 in the nozzle: body 34, the electrolyte 18 uniformly
strikes the entire surface of the body 15 to be coated which
is moving opposite to the flow direction.
In so doing, the oppositely directed movement vectors of
the body 15 are added to those of the injected electrolyte 18
and, by means of the jet action of the bore holes 44 at the
surface of the body 15 to be coated, cause a turbulent flow
acting along the entire surface. The diffusion layer
occurring during galvanization is practically completely
destroyed by this turbulent flow.
The pressure of the electrolyte 18 in the nozzle body 34
is maintained constant. along its entire length by means of the
diaphragms 36 with their stepped through-openings 37, which
diaphragms 36 are arranged between the respective region
planes 11 of the bore holes 44. At the same time, these
diaphragms act as locally defined shoots for the electrolyte
18, so that, with rest>ect to the galvanizing process, a
current flow is generated which acts on the body 15 in a
pulsed manner.
As a result of these steps, current densities of 10 to
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400 A/dm2 can be selected between the electrolyte 18 and the
' surface of the body 15 to be coated in the present example of
galvanic zincing. In this way, the galvanic coating process
is accelerated in comparison to the previously known processes
and substantially thicker layers can be applied per unit of
time than was previoua~~ly possible.
The purpose of the guide ring 26 is to prevent a short
circuit between the body 15 and nozzle body 34. Such a short
circuit would come about if the body 15 were to contact the
nozzle body 34 owing t.o the relative movement between the body
and electrolyte 18 and the resulting oscillations.
Of course, it 1S possible to use a smaller or greater
number of region planes 11 than was described in this
embodiment example depending on quality requirements,
15 materials used or type: of alloy.
